On Sun, Feb 17, 2013 at 3:21 AM, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > On Sat, 16 Feb 2013, Hugh Dickins wrote: >> On Sat, 16 Feb 2013, Linus Torvalds wrote: >> > >> > I think it's worth it to give them a heads-up already. So I've cc'd >> > the main suspects here.. >> >> Okay, thanks. >> >> > >> > Daniel, Dave - any comments about a NULL fb in >> > intel_choose_pipe_bpp_dither() during either suspend or resume? Some >> > googling shows this: >> > >> > https://bugzilla.redhat.com/show_bug.cgi?id=895123 >> >> Great, yes, I'm sure that's the same (though it says "suspend" >> and I say "resume"). >> >> > >> > which sounds remarkably similar, and is also during a suspend attempt >> > (but apparently Satish got a full oops out).. Some timing race with a >> > worker entry? > > Comparing Satish's backtrace and drivers/gpu/drm history, it's clear that > the oops comes from Daniel's 3.8-rc2 45e2b5f640b3 "drm/i915: force restore > on lid open", whose force_restore case now passes down crtc->base.fb. But > I wouldn't have a clue why that's usually non-NULL but occasionally NULL: > your timing race with a worker entry, perhaps. > > And 45e2b5f640b3 contains a fine history of going back and forth, so I > wouldn't want to play further with it out of ignorance - though tempted > to replace the "if (force_restore) {" by an interim safe-seeming > compromise of "if (force_restore && crtc->base.fb) {". Two things to try while I try to grow a clue on what exactly is going on: 1. Related to new ACPI sleep states we've recently made the lid_notifier locking more sound, maybe that helps: http://cgit.freedesktop.org/~danvet/drm-intel/commit/?h=drm-intel-next-queued&id=b8efb17b3d687695b81485f606fc4e6c35a50f9a 2. The new i915 force restore code is indeed missing a safety check compared to the old crtc helper based one: diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 6eb3882..095094c 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -9153,7 +9153,13 @@ void intel_modeset_setup_hw_state(struct drm_device *dev, if (force_restore) { for_each_pipe(pipe) { - intel_crtc_restore_mode(dev_priv->pipe_to_crtc_mapping[pipe]); + struct drm_crtc * crtc = + dev_priv->pipe_to_crtc_mapping[pipe]; + + if (!crtc->enabled) + continue; + + intel_crtc_restore_mode(crtc); } i915_redisable_vga(dev); The issue is that we save a pointer to the fb (since those are refcounted) but copy the mode into the crtc struct (since modes are not refcounted). So on restore the mode will always be non-NULL, which is wrong if the crtc is off (and so also has a NULL fb). The problem I have with that patch is figuring out how this ever worked. I think I need more coffee ;-) Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
